Commercial and government information providers serve a wide variety of web resources to requesting client devices. For example, banks and retailers operate sophisticated web sites and serve mark-up code and associated CSS code and JavaScript code from their web server systems to potential customers. Such web sites may seek private information from users and carry out monetary transactions, such as by obtaining information about credit card of banking accounts for the transfer of money. Illicit organizations attempt to interfere with such transactions, such as to obtain access to monetary accounts of users or to have goods surreptitiously delivered by associates of the illicit organizations.
For example, it is common for illicit organizations to cause malware to be installed on numerous client computers without the knowledge of the owners and operators of those computers. As one example, known as a “man in the middle” attack, that malware may present itself to a user as if it is legitimate software from a bank, retailer, or other provider, and may then cause the user to pass it private information (e.g., social security number and credit card number), and may then pass different information to the relevant information provider (e.g., having money transferred from the user's account to another account, while showing the user transaction information that looks legitimate).